The trading watchdog warned six debt management companies and four cold-calling firms to stop using unsolicited and misleading calls to advertise their services.

The Office of Fair Trading today said the firms, which cannot be named, must stop making the calls or face formal enforcement action.

The warning came after the OFT and the Information Commissioner's Office received a large number of complaints from consumers who had been cold-called by the firms. In some cases people were called despite registering with the Telephone Preference Service, which enables consumers to opt out of receiving unsolicited sales and marketing phone calls.

The trading watchdog also found that most of the information given in the calls was potentially misleading or inaccurate, or it failed to give important information about the purpose of the call and the caller's identity.

It said in some cases the calls misled consumers into believing they were one of a "few chosen individuals" who had been contacted as part of a Government scheme to help wipe out consumer debt.

In other cases people were transferred to a commercial debt management business on the pretext of talking to a not-for-profit debt adviser.

But once they had been transferred to a different business they were often not told that they would have to pay a fee for both the initial advice they received and the debt solution offered.

Nigel Cates, deputy director of consumer credit at the OFT, said: "Taking advantage of people who are suffering distress through debt problems is completely unacceptable and this practice of illegal or misleading cold-calling for debt management services must cease immediately."